This guide shows you how different illumination and specular values affect the look of your structures during night time. It's primarily intended for asset creators and serves as a visual reference only. This is in NOT a 1-2-3 tutorial or how-to! The guide will be updated as we learn how to deal with artifacts and other texturing related elements. If you've encountered anything in particular yourself, please share it with all of us!

To start, I'm going to quote Dev Diary 2 and the Asset Editor wiki pages.
This is all the info that's already out there.



''The likelihood of a window to be lit at a given time and its intensity are randomized for values within 128 and 255, the closer the value is to a boundary the more likely it is to be lit and stronger.''

Source: http://www.skylineswiki.com/Asset_Editor

''It used to be the illumination map acts as a mask where a value of 0 (black) means no illumination and a value of 255 (white) means full illumination using the diffuse texture information.
We preserved this behaviour but squeezed the color value to range between 0 and 120 instead, where 0 still mean no illumination contribution from the diffuse texture and 120 means full contribution. We hereby freed the range 128 to 255 to allow windows to be lit randomly. A value of 192 means neutral, so if you want a building to be unlit at all times, the illumination map needs to be solid 192. The likelihood of a window to be lit at a given time and its intensity are randomized for values within 128 and 255, the closer the value is to a boundary the more likely it is to be lit and stronger.''

Source: https://forum.paradoxplaza.com/forum/index.php?threads/cities-skylines-after-dark-dev-diary-2-whats-new-with-modding.878916/

This guide originally started out as a quick experiment. But with the incredible amount of possibilities you get with the randomized lighting, as well as existing specularity and illumination during daytime, it can be very hard to predict how assets are going to look in the end.

As such, I've setup the following textures.










These are applied to a simple 4x4 box. I may add alternative overviews later on.


Due to the unpredictable behavior of the lighting system (which is a good thing!) you can only analyze the final look by placing lots and lots and lots of these. So be prepared for a lot of screenshots on the next pages!

Down below you will find a few screenshots of what this will look like in the asset editor, during different times of day. Again, you will notice the randomness for values 128 to 255. That's why you will want to test your assets ingame or even reload the editor a few times to see if you're gaining or losing light at any instance.

• Notice the differences left and right...

Also notice values closer to 128 and 255 don't guarantee the lights are always on. They seem to have a bigger influence on overall brightness. If you want your windows lit constantly, you will have no choice but to go below 127, which will obviously mean some lighting during daytime.

I'm going to refrain from a lot of text here, because I think the images speak for themselves...

A bunch of them next to each other:


Ignore the block on the right, I think it had no power.







I think we can all agree how amazing this looks, even on a flat polygon! Notice values 128 and 255 look like they are connected to different seeds, so it does matter if you go above or below 192. It's hard to analyze to what extent though...

Here's two video comparisons created by stmSantana:

• Combining lights with a strong specular on a horizontal surface results in a kind of z-fighting:

• Transition areas will create very obvious artifacts and overlap problems:

This may also occur during daytime when the engine decides certain pixels are inside or outside the illuminated area. Pixel precision does not solve this, and it becomes more and more visible as you zoom away and the texture resolution is lowered to LOD levels (mipmaps). This causes severe aliasing and you will be left with light emitting jaggies and edges around every window.

That's about it for now guys! I'm gonna share this guide as is so people can look into it, I'm sure it'll grow larger as we learn how to use the illumination properly...

Thanks for checking this out & thank you to CO for implementing this system!